Apparatus is well known for protective coating of sheets and strips on both sides by galvanizing, tinning aluminizing etc. Such apparatus consists of treatment lines comprising strip uncoilers, facilities for surface treating both sides before coating, facilities for applying the coating, facilities for finishing the coated materials and handling facilities for the coated strips or sheets. There are many classic examples of commercial two-sided coating production lines for galvanizing and aluminizing. However, on such conventional two side coating production lines, it is not possible to directly apply such protective coatings to only one side of the treated material. For single side coating such as galvanizing, special complex lines have to be designed, including different solutions for surface pretreatment, special adaptations for applying the zinc and special facilities for finishing the product. These adaptations for single coating are complicated as compared to the conventional two-sided coating apparatus.
For example, in order to apply on one side only of the ZINCROMET.RTM. protective coating, specified and widely used in the automotive industry utilizing DECROMET.RTM. primer, the line would require a special roll coater to apply the Decromet primer to only one side of the sheet surface; a special drying oven for said applied primed one side; a second roll coater for applying the Zincromet coating to the single primed surface; a second oven to heat treat this coating and also a cleaning machine to clean the uncoated surface, if necessary.
For the application of GALVA-ONE.RTM. electrolytically applied coating or the similarly applied UNIKOTE.RTM. coating, would require special electrolytic production lines comprising baths for electroplating these coatings from appropriate baths with specially located and positioned electrodes and special electrical connections to the treated strip.
For the production of one side only hot dipped galvanized coatings on sheet or strip by the ZINCGRIP.RTM. coating method or the OGUS.RTM. coating procedure would require special bath arrangements for forming the stationary wave in the molten zinc for requisite control to coat one side of the sheet only, followed by special washing apparatus for the one side coated strip or sheet.
As can be seen, such modified apparatus for single side coating is very expensive due to its complexity and because of its special nature, having only a single use, is not commercially available.
Polish patent application No. 217,065 filed in 1979 is directed to a method of single side protective coating with conventional coatings of zinc, aluminum or tin. That method relates to uncoiling and parallelly juxtaposing two strips and then passing said strips through a coating bath under such a front-tension and back tension at the entry and exit of the coating bath that a tight contact of juxtaposed strips is obtained, making it impossible for the bath to enter between said strips.
With this method of No. P. 27065, it is not always possible to obtain a sufficiently tight contact between the strips to exclude the bath. However, based on the principles of No. P. 27065, a further development is possible wherein after juxtaposing the two strips the adjacent edges are joined by welding or other durable joining means thus obtaining a durably joined double strip. The double strip is then conventionally pre-treated on both sides as a single strip and is then conventionally continuously coated on both sides, e.g. by dip galvanizing. As a result a two sided galvanized double strip is obtained. This double strip composite consists of two strips each coated on only one side. This doubled strip is then finished by separating into two separate strips by trimming along the joined edges. As can be seen, this method permits achieving the same result as with the present invention by continuous discrete operations but this patent does not reveal any specific apparatus for realizing the results.